In a certain type of rock drill, housing parts are held together by bolts with threads in both ends of the bolts and an eccentric collar, which enables a part of the housing to be demounted while the second housing parts are held held together. The eccentric collar constitutes a basis for an axial biasing force. The eccentric collar locks the bolt in rotational direction in a part of the housing together with a cylindrical surface of the bolt closest to the collar. Thereby may a nut be loosened at the same time as biasing of the other housing parts is maintained.
When the eccentric collar together with the cylindrical surface of the bolt locks the bolt in rotational direction large normal forces occurs in contact points; between the cylindrical surface of the bolt and the housing part, respective between the eccentric collar and the housing part. This cause wear damages on the cylindrical surface of the bolt when the rock drill vibrates during operation. These wear damages may initiate fatigue cracks causing fracture of the bolt.